The present invention relates in general to converting signals between the analog and the digital domains and, more specifically, to an analog-to-digital converter or a digital-to-analog converter wherein two separate signals are added together prior to conversion and are separated from each other after conversion so as to convert both signals using only a single converter.
Digital signal processing (DSP) is being adopted in many electronics applications, such as digital audio, signal measurement and analysis, and communications, for example. DSP uses specialized microprocessors which are adapted to perform signal processing functions digitally and at a high rate of speed. DSP achieves advantages in programming flexibility, inherent stability, increased accuracy, high reliability, and lower cost.
Most frequently, systems employing DSP have analog input signals and/or output signals. This requires conversion between the analog and digital domains, such as with an analog-to-digital (A/D) converter and a digital-to-analog (D/A) converter, both of which are referred to generically herein as analog-digital converters. In the context of the digital audio example, radio receivers are known which obtain an analog radio signal from an antenna, generate an analog intermediate frequency (IF) signal in a tuner, digitize the IF signal, demodulate and further process the resulting audio signal in DSP, convert the audio signal back to an analog signal, and reproduce analog audio signals using an amplifier and speakers. Besides the analog IF signal, the DSP processing typically will employ other analog inputs, such as data inputs from the tuner (e.g., received signal strength) or command signals (e.g., volume, tone or balance controls). Thus, it is often necessary to digitize a number of different input signals.
Analog-digital conversion can be achieved using stand-alone A/D or D/A integrated circuits (ICs). Each IC has an associated part cost and requires its own signal path into the DSP IC, supporting functions (such as a clock), and separate packaging space. Thus, it is desirable to minimize the number of analog-digital converters to be used.
DSP ICs are also produced with some A/D and D/A converters already included on the integrated circuit. Since the number of such converters is limited, it is necessary to utilize them as efficiently as possible.
It is known to share a single analog-digital converter between two or more signals by time multiplexing the converter. However, such converters and the associated multiplexing components are complicated, have increased costs, and reduce the sampling rate that may be utilized with each of the multiplexed signals.